A mass spectrometer is a highly complex array of components. These components include an extensive ultra high vacuum system, composed of stainless steel housings, precision-fit flanges and gaskets, high performance valves, and a variety of ultra high vacuum pumps and gauges. Magnetic-sector type instruments require one or more high-quality magnets with precise controllers. Solids units use thermal ionization sources, requiring multiple power supplies and controls to produce sample ions and focus them into a path through the magnetic field. Other specialized components collect and measure the ions. This requires additional precision equipment, including systems that can accurately and reproducibly measure extremely small electrical currents. The ultra high vacuum, magnet, source, and collector units all require monitoring and control electronics.
An electronic interface is required between the analog hardware of the instrument and the computer dedicated to analyzing samples. The computer adds yet another set of hardware components, such as power supplies, memory, a central processor, as well as the interfaces with the computer peripherals such as the printer, console, and mass memory. Finally, system software and applications programs must be provided to issue commands to operate the instrument hardware.
All of these components must be working properly to provide timely, high quality data. But because of the wide range of integrated components, root causes for problems on a mass spectrometer can be difficult to diagnose. Locating the weak link can be an intricate and time-consuming effort. Moreover, a single problem may impact several individual subsystems. Also, minor weaknesses in several subunits that would not cause a failure individually could combine synergistically to create a problem.
Prior practice in mass spectrometry has included two basic strategies for handling instrument problems. Examples of prior practice are exemplified by "Incos 2000 Series Data Systems for Mass Spectrometry," by the Finnigan Corporation and "Application of Artificial Intelligence to Triple Quadrupole Mass Spectrometer," by C. M. Wong, et al, IEEE Transactions on Nuclear Science, Vol. NS-31 (Feb. 1984). The most common practice is to wait until a component has clearly failed, and then perform tests to identify the root cause or causes. More experienced practitioners might be able to discern less obvious symptoms and thereby predict some failures, but this is neither common nor all-encompassing. In some cases, computerized test protocols may be available to the diagnostician, and he may be able to recall component status information from electronic storage. The second basic strategy employs pre-set status conditions to alert the operator to developing problems. Violations of these set points can either signal a warning, or shut the system down. These strategies have several deficiencies. Obviously, a component failure is detected most often during an actual analysis. This not only costs the time involved in that analysis, it also causes delays in providing results for the sample. Once the failure has occurred, more time will be lost while tests are run and diagnostic information is collected. The practitioner then needs to evaluate the results, perhaps perform more tests, and then devise a repair plan. If the practitioner is not fully qualified to handle certain problems, additional experts may need to be consulted.
Not only time is lost but running a component to failure may cause damage that could have been avoided by an earlier shutdown. For example, if a typical ultra-high vacuum diffusion pump ran for several hours at 0.050 Torr, it could be severely damaged and might well be destroyed. Yet operation at 0.003 Torr would bake the unit but probably cause no permanent harm. This is, in fact, a major part of the rationale behind the set-point shutdown strategy.
Unfortunately, the latter approach tends to be quite inflexible. It will ignore almost-critical values, yet flag a high reading that lasts only a fleeting moment. Delay circuits may be used to screen out some transients, but these are usually set quite conservatively to avoid potentially damaging conditions. This conservatism tends to cause false alarms and unjustified shutdowns. Also, such a system cannot evaluate situations where a combination of minor instabilities may predict a major problem. Finally, even a valid shutdown done too abruptly might impact other parts of the instrument.
Therefore, it is an object of this invention to combine elements of real-time instrument automation, set-point damage prevention, and expert system technology to monitor the operation of a mass spectrometer.
A further object of this invention is to collect real-time status data for all key instrument components, evaluate the results using a rule base of expert knowledge, and alert the operator to developing problems.
A still further object of this invention is to immediately provide an up-to-date chronology of the status information and suggest additional diagnostic tests when a major problem to the system is detected.
It is a further object of this invention that during a troubleshooting session, the system would employ the knowledge of several experts, not just one person.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.